Exploring Terraform Outputs

Viewing the output file#

We’ll retrieve the nodes of the newly created Kubernetes cluster and see what we got. But, before we do that, we need to create a kubeconfig file that will provide kubectl the information on how to access the cluster. We could do that right away with gcloud, but we’ll make it a bit more complicated.

To create kubeconfig, we need to know the name of the cluster and the region and project in which it’s running. We might have that information in our heads. But, let’s imagine that’s not the case. What if we forgot it, or didn’t pay attention before? That gives us a perfect opportunity to introduce yet another Terraform feature.

We can define outputs with the information we need, as long as that information is available in Terraform state.

We’re specifying which data should be output by Terraform. Such outputs are generated at the end of the terraform apply process, and we’ll see that later. For now, we’re only interested in the outputs so we can use them to deduce the name of the cluster, the project ID, and the region, so that we can retrieve the credentials for kubeconfig.

If we want to see all the outputs, we can simply refresh. That updates the state file with the information about the physical resources Terraform is tracking and, more importantly, shows us those outputs.

The output, limited to the relevant parts, is as follows.

We can clearly see the name of the cluster, the project ID, and the region. But that’s not what we really need. We’re not interested in seeing that information, but rather in using it to construct the command that will retrieve the credentials. We can accomplish that with the terraform output command.

We can see that the output is devops-catalog.

Checking the cluster#

Now we know how to retrieve the output of a single value, so let’s use that to construct the command that will retrieve the credentials.

We specified that kubeconfig should be in the current directory by exporting the environment variable KUBECONFIG. Later on, we retrieved the credentials using gcloud. What matters, apart from the obvious need to retrieve the credentials, is that we used terraform output to retrieve the data we need and pass them to gcloud.

The only thing left is to give us admin permissions to the cluster.

Now we should be able to check the cluster that Terraform created for us. We’ll retrieve the nodes using the following commands.

The output states that “No resources were found in default namespace.” That’s expected. We retrieved the nodes of the cluster, and we got none. GKE does not allow us to access the control plane. On the other hand, we haven’t yet created worker nodes, so there are none for now.

Try it yourself#

You can try all of the commands used in this lesson in the code playground below. Press the “Run” button and wait for a few seconds for it to connect.

For ease of use, all of the commands above are combined in main.sh.